The conventional melt spinning pack used for producing synthetic fibers comprises the following parts.
The pack comprises a cylindrical pack case opened in the bottom surface and the top surface, and a spinneret having many spinning holes, a pressure plate having many polymer flowing holes, a wire mesh filter, a cylindrical filter medium containing-spacer, a granular filter bed (usually called a sand bed) contained inside the spacer, and also a pack cap having a polymer introducing hole at the center for introducing a molten polymer and installed to close the top surface of the pack case, respectively contained in this order from bottom to top in the pack case, and also has a first space formed between the bottom surface of the pack cap and the top surface of the granular filter medium, and a second space formed between the top surface of the spinneret and the bottom surface of the pressure plate.
The pack case, spinneret, pressure plate, filter medium-containing spacer and pack cap are usually respectively made of metal.
The granular filter bed is usually a layer of sand consisting of stainless steel particles, glass particles or quartz particles.
The molten polymer as a raw material for producing synthetic fibers is introduced into the first space from the polymer introducing hole formed at the center of the pack cap, passes through the granular filter bed (sand bed) and the wire mesh filter, and further through the many polymer flowing holes of the pressure plate, flows into the second space, and reaches the many spinning holes of the spinneret.
The molten polymer flowing into the many spinning holes passes through these spinning holes and is spun from the spinning holes to form many filaments. The filaments are cooled to form a yarn comprising the multifilament. The yarn is wound around a bobbin installed on a winder. Thus, synthetic fibers are produced.
In some cases, the many filaments are divided into several groups, say, 2 to 4 groups, and the many filaments of each group are formed as one yarn respectively. In this case, from one melt spinning pack, a plurality of, that is, 2 to 4 yarns are produced.
The conventional melt spinning pack has the following problems.
The flowing of polymer which is introduced through the polymer introducing hole provided at the center of the pack cap and flowed into the first space and further come into the granular filter bed (sand bed) is distributed densely in the central region thereof and is less likely to reach the peripheral region. So, the many filaments obtained from the many spinning holes of the spinneret become different from each other in filament diameter and it causes a problem of unevenness of fineness.
Furthermore, the granular filter bed (sand bed) has avoid volume of usually about 40% therein. This means that the granular filter bed (sand bed) has a void of about 40% to allow polymer flow. This structure elongates the dwell time of the polymer in the granular filter bed (sand bed). As a result, the passing time of polymer from introducing from the polymer introducing hole of the pack cap to spinning from the many spinning holes of the spinneret, i.e., the dwell time of the polymer in the pack becomes long. If the dwell time is long, the polymer is deteriorated during the dwell time. The deterioration of the polymer occurs locally in the pack, and at the places at which the polymer is deteriorated and to which the deteriorated polymer moves, it remains in the pack to cause abnormal dwelling. The abnormal dwelling in the pack also causes the filaments to be uneven in fineness. Furthermore, if the deteriorated polymer is spun from the spinning holes, the obtained filaments become irregular in quality in the longitudinal direction, and the filaments are broken before arriving at the winder.
On the other hand, Japanese Publication (Kokaku) No. SHO 39-24309 proposes the following idea for a melt spinning pack.
The spinning pack has a flow arranging plate provided with many flow arranging holes and having a concave bottom surface. The structure is intended to make different in length the many flow arranging holes between the top surface and the bottom surface of the flow arranging plate and to produce uniform polymer flow to the spinneret having many spinning holes.
However, it was found that even if fibers were produced by using the spinning pack, the obtained fiber bundle had relatively great difference of fineness between the filaments. One of the reasons is estimated to be that the space formed between the bottom surface of the flow arranging plate and the top surface of the spinneret has a form likely to cause abnormal dwelling of the polymer.
The above problems of the conventional melt spinning packs arise more remarkably when a yarn is produced from a molten polyester containing an electro-control agent.